Solar and/or battery powered parking systems such as single-space or multi-space meters for vehicles can employ parking meters with vehicle detection systems that detect the presence of a vehicle in a parking space. Time paid for parking in the space can then be dependent on the space being occupied by a vehicle. One technique for detecting the presence of a vehicle is to use a magnetometer located in the parking space. A magnetometer can be advantageous because it has relatively low power requirements, and often can be suitably powered by a battery. A magnetometer must be located close to the vehicle that will occupy the parking space, for accurate detection without false indications. Placement of a magnetometer in a parking space typically requires coring of the surface asphalt or concrete (i.e., drilling a cylindrical opening or shaft) for embedding the magnetometer in the adjacent street or sidewalk area. This can be a very labor intensive and relatively expensive proposition.
Alternatively, a magnetometer could be included in a parking meter of the parking space, which would avoid the surface coring and embedding of the magnetometer. This placement will usually decrease the accuracy of detection, because magnetometers possess no directional detection capability. Because of the directional deficiency, a magnetometer installed in a meter potentially could not distinguish between a vehicle parked in the space associated with the parking meter and a vehicle parked in an adjacent parking space, or could not distinguish between a vehicle parked in the space and a vehicle stopped in the street.
Other vehicle detection systems have employed ultrasonic or infrared systems internal to a parking meter. Such systems send out a known ultrasonic or infrared signal and evaluate vehicle presence based on partial reflection of the signal, or lack thereof. The signal can be modulated for improved accuracy of detection. Because parking meters, especially single-space parking meters, usually have a limited power budget, these ultrasonic and infrared systems are designed to be operated at relatively low power levels. Unfortunately, low-power ultrasonic and infrared systems are often prone to signal interference, due to pedestrian traffic, rain, snow, wind, and the like, and can have very narrow angles of detection. Accuracy of detection can be improved by increased signal power. Moreover, ultrasonic and infrared systems typically require a relatively large percentage of the transmitted signal to be reflected back for detecting the presence of a vehicle. Receiving a reflected signal that constitutes a large percentage of the transmitted signal can be problematic, given weather conditions and pedestrian traffic, and therefore ultrasonic and infrared systems can be inherently unreliable as a means for detecting the presence of a vehicle in a parking space.
Other vehicle detection systems that potentially could be more accurate than low-power magnetometers, ultrasonic systems, and infrared systems, include cameras, passive infrared systems (such as used in automatic door openers), active infrared detection, and radar. These other systems, while possibly providing very accurate detection of a vehicle in a parking space, typically use more power than can be provided by a battery, solar cell, or other low-power system of a battery and/or solar powered parking meter such as the single space meter described below. For example, radar can be very difficult to utilize because of power management issues, and often provides relatively unpredictable results.
It should be apparent that accurate vehicle detection systems either require extensive installation and/or maintenance costs, as with embedded magnetometer systems, or are very inaccurate when placed a distance away from the object to be detected, or use too much power for a single-space parking meter in order to be suitable. In addition, a directional sensor that is placed in the space to be monitored or external to a meter pole, may become compromised by dirt or debris, or may fall victim to tampering. What is needed is a more reliable, low power vehicle detection system for use in a solar and/or battery powered parking meter. The present invention satisfies this need.